DNA fragment carrying the gene encoding the enzyme for fragmenting n-acetylheparosan and the adjacent sequences permitting its expression, recombinant enzyme intended for fragmenting n-acetylheparosan and its use

ABSTRACT

The invention relates to a DNA fragment of SEQ ID NO: 1 herein and encoding the SEQ ID NO: 2 peptide sequence herein. This DNA sequence carries the gene encoding the enzyme for fragmenting N-acetylheparosan and the adjacent sequences permitting its expression. The invention also relates to an enzyme intended for fragmenting N-acetylheparosan derived from this gene and the processes for fragmenting high molecular mass N-acetylheparosan using this enzyme.

The present invention relates to a DNA fragment carrying the gene encoding the enzyme for fragmenting high molecular mass across N-acetylheparosan and to the adjacent sequences permitting the expression of this gene, a recombinant enzyme intended for fragmenting N-acetylheparosan containing this gene, the production of preparations containing this recombinant enzyme as well as processes for fragmenting N-acetylheparosan using this enzyme.

It is known that some bacteria of the Escherichia coli species produce a capsular polysaccharide, normally called K5, which is a family of polymers consisting of repetitive β-D-glucuronyl-1,4-α-N-acetyl-D-glucosaminyl units (1,4) (W. F. Vann et al., Eur. J. Biochem, 1981, 116, 359-364), of structure (a): ##STR1##

This polysaccharide will be called here "N-acetylheparosan". This product has at the level of the "uronic acid" units, a regular structure composed only of D-glucuronic acid. Its molecular mass is between 10⁵ and 2.10⁶ Da. It is therefore an N-acetylheparosan of high molecular mass.

N-acetylheparosan is useful as raw material for the pharmaceutical industry but, for this use, it has a too high molecular mass. As example, reference can be made to Patent Applications EP-0,333,243 and EP-0,489,647 which relate to low molecular mass N-acetylheparosan derivatives or to products obtained from low molecular mass N-acetylheparosan. The various products described in these two applications possess highly valuable pharmacological properties. Their molecular masses are less than or equal to 15,000 Da.

It is known that N-acetylheparosan (K5 polysaccharide) can be fragmented by a phage lyase derived from a phage specific for the Escherichia coli strain (K5), but this fragmentation is very extensive and leads to a substantial disappearance of the fragments with a molecular mass of 5,000 Da into much smaller chains, with molecular masses of less than 1,000 Da (D. Gupta et al., FEMS Microbiology Letters, (1983), 16, 13-17). This type of fragmentation is used in Patent Application EP-A-0,333,243 for the preparation of fragments containing a maximum of 10 saccharide units.

It has also been observed that cultures of Escherichia coli (K5), strain SEBR 3282, produce under certain environmental conditions, an enzyme which fragments N-acetylheparosan during culture in a fermenter. The strain SEBR 3282 of Escherichia coli (K5) responds positively to the typing test with the K5-specific phage, according to the method of B. Kaiser et al. (J. Clin. Microbiol., (1984), 19, 2, 264-266). It is therefore indeed an Escherichia coli (K5) strain. This strain was deposited at the Collection Nationale de Cultures de Microorganisms (CNCM) of the Institut Pasteur, Paris, France, under N° 1-1013.

The enzyme obtained from the strain SEBR 3282 of Escherichia coli (K5) has a molecular mass of between 62,000 and 70,000 Da (measured by exclusion HPLC), its isoelectric point is situated in the pH region of between 4.7 and 5.4 pH units and it is an eliminase.

This enzyme is also characterized in that it acts in the following manner:

it is of membrane origin,

the temperature for its optimum operation (maximum activity) is close to 37° C. and the temperature at which it is inactivated is about 60° C.,

the optimum zone of pH for its operation is situated between the pH 6 and pH 7 values,

for its operation, the optimum zone of concentration of monovalent or divalent ions is situated in the vicinity of 0.2 M.

The enzyme obtained from the abovementioned strain is capable of acting on high molecular mass N-acetylheparosan and of fragmenting it in the absence of bacterial body in vitro and makes it posible to obtain, under certain conditions, N-acetylheparosan fragments situated around a peak with a molecular mass of about 5,000 Da, corresponding to within a few disaccharide units, about 70% of the product.

It was observed, moreover, that a preparation of this enzyme suitably solubilized, makes it possible to obtain fragments of higher molecular mass compared with the fragments obtained spontaneously, that is to say with the non-solubilized enzyme. Indeed, preparations of solubilized enzyme make it possible to modulate the fragmentation and to obtain fragments of which the majority has a molecular mass greater by at least 1,000 to 3,000 Da compared with the molecular mass of the fragments obtained spontaneously.

However, the industrial use of this enzyme and in particular in a soluble form and preparations containing it is limited by the small quantities available from the strain SEBR 3282 of Escherichia coli (K5).

Moreover, the production of preparations of the solubilized enzyme requires a number of operations such as the solubilization of the enzyme by means of detergents or strong inorganic bases. These manipulations also increase the cost of preparing the various low molecular mass N-acetylheparosans used as raw material in the pharmaceutical industry.

To overcome these disadvantages, research studies in this domain have been carried out and have permitted the isolation of a DNA fragment carrying the gene encoding an enzyme for fragmenting high molecular mass N-acetylheparosan. The introduction, into an expression vector, of the DNA fragment carrying the sequence encoding the enzyme has made it possible to obtain large quantities of a recombinant enzyme intended for fragmenting high molecular mass N-acetylheparosan.

Surprisingly, it was observed that starting with this same DNA fragment it is possible to obtain the recombinant enzyme in two different forms: the first form of the enzyme is associated with the cellular pellet (that is to say about 90% of the enzymatic activity) and is termed membrane form like the enzyme obtained from the wild-type strain; the second form of the enzyme is present spontaneously in the supernatant, in a substantial quantity and is termed soluble form.

Indeed, it was observed that a nucleotide sequence of the cloned DNA fragment makes it possible to obtain constructs spontaneously expressing a high percentage of the enzyme being in a soluble form, that is to say directly in the culture supernatant. The soluble form of the enzyme prepared from the culture supernatant and used under defined conditions makes it possible to fragment the high molecular mass N-acetylheparosan completely and precisely into fragments assembled around a predominant peak corresponding to 9-10 disaccharide units, which corresponds to a molecular mass of about 5,000 Da, evaluated by exclusion HPLC. The dispersion of the fragments around this predominant peak is very low. A disaccharide unit of N-acetylheparosan corresponds to the disaccharide unit represented by the formula (a).

This possibility, of obtaining N-acetylheparosan fragments weakly dispersed at the level of their molecular mass, offered by the recombinant enzyme in a soluble form, dispenses from any subsequent fractionation whatsoever, especially by exclusion chromatography.

Furthermore, by modifying the operating conditions, it is possible, still by resorting to the soluble form of the enzyme, to obtain N-acetylheparosan fragments of size less than or greater than the 9-10 repetitive disaccharide units mentioned above. To obtain fragments whose size is less than the 9-10 repetitive units, it is also possible to use, in particular, the membrane forms of the enzyme.

Moreover, irrespective of the form, soluble or membrane, of the enzyme, the enzymatic reaction can be carried out incompletely in order to obtain a mixture of fragments of sizes greater than the 9-10 disaccharide units mentioned above.

The present invention therefore relates to a DNA fragment carrying a gene encoding the enzyme intended for fragmenting a high molecular mass N-acetylheparosan, the recombinant enzyme encoded by this gene, the various forms of the recombinant enzyme derived from this sequence, especially the membrane form and the soluble form of this enzyme, as well as fragmentation processes using this recombinant enzyme.

The DNA fragment carrying the gene encoding the enzyme intended for fragmenting N-acetylheparosan and the expression systems permitting its biosynthesis, corresponds to the sequence SEQ ID N° 1.

FIG. 1 depict a double-stranded nucleotide sequence, which is supplemented with a reading frame of 820 amino acids.

This DNA fragment, whose exact size is 3089 base pairs (bp) carries the gene encoding the enzyme for fragmenting high molecular mass N-acetylheparosan, but also the regulatory signals permitting its expression. These regulatory signals are mainly:

1-a specific promoter, which is essential for the transcription of the gene

2-a ribosome-binding site which is essential for carrying out the translation of the protein from the transcribed mRNA.

Computer analysis reveals several reading frames. Reading frame is understood to mean an amino acid sequence deduced from the nucleotide sequence via the genetic code which starts with a methionine coded by ATG and which ends with one of the stop codons TAA, TGA or TAG.

Several possible reading frames whose size is less than 100 amino acids exist in this DNA fragment. There is also a reading frame of 820 amino acids characterized in that it has the peptide sequence SEQ ID N° 2.

The sequence SEQ ID N° 2 is also the subject of the present invention.

The invention also relates to any DNA fragment comprising the reading frame or part thereof which gives the peptide sequence or derived from the peptide sequence.

The invention also relates to a strain carrying a plasmid permitting the production of a recombinant enzyme which fragments high molecular mass N-acetylheparosan. Such a strain has been deposited under the Budapest Treaty at the CNCM of the Institut Pasteur, Paris, France on 6 Aug. 1993, under the number 1-1352.

The strain carrying a plasmid permitting the production of a recombinant enzyme which fragments high molecular mass N-acetylheparosan is a recombinant strain from the strain RRI of Escherichia coli (K12) provided by GIBCO-BRL (ref. 530-8231 SA). Other appropriate Escherichia coli strains can be envisaged.

As vector, there has been used the vector pUC 18 hydrolysed by BamHI/BAP (Pharmacia® ref. 27-4855-01), into which the DNA fragment corresponding to the sequence SEQ ID N° 1 has been introduced.

However, to obtain a strain carrying a plasmid permitting production of a recombinant enzyme which fragments high molecular mass N-acetylheparosan, it is possible to envisage the use of other vectors and/or as indicated above, of other recipient strains.

As other vectors, it is possible to use vectors such as pBR 322 (Pharmacia® ref. 274902-01) or any other vector into which it is possible to insert all the DNA fragment corresponding to the sequence SEQ ID N° 1 or part of-this DNA fragment carrying the sequence necessary for the expression of the protein of 820 amino acids, this translated sequence being the sequence SEQ ID N° 2.

Apart from the recipient strain RRI of Escherichia coli (K12), other Gram-negative strains can be used provided however that the regulatory system for the protein containing 820 amino acids and having the peptide sequence SEQ ID N° 2 is compatible with the host cell.

The strain deposited at the CNCM of the Pasteur Institute, Paris, France, on 6 Aug. 1993 under the number 1-1352 is a strain obtained by transforming the strain RRI of Escherichia coli (K12) with a vector carrying a DNA fragment corresponding to the sequence SEQ ID N° 1 and therefore, carrying the sequence necessary for the expression of the protein of 820 amino acids which is the sequence SEQ ID N° 2 (translated sequence).

However, it is possible to envisage a number of strains which produce a recombinant enzyme intended for fragmenting high molecular mass N-acetylheparosan which is obtained by transforming the strain RRI of Escherichia coli (K12), or other suitable Gram-negative strains, with vectors carrying DNA fragments derived from the SEQ ID NO: 1 sequence and carrying at most the sequences necessary for the expression of the protein of 820 amino acids. These translated sequences are:

either the sequence SEQ ID N° 2 as a whole , corresponding to amino acids 1 to 820,

or the entire amino acids 112 to 820 of the sequence SEQ ID N° 2,

or the entire amino acids 160 to 820 of the sequence SEQ ID N° 2,

or the entire amino acids 194 to 820 of the sequence SEQ ID N° 2.

The invention therefore relates in particular to a DNA fragment encoding all or part of the sequence SEQ ID N° 2 as indicated above.

The invention relates, in particular, to a gene encoding an enzyme intended for fragmenting N-acetylheparosan which is carried by the DNA fragment of the nucleotide sequence.

The invention relates more particularly to a recombinant enzyme intended for fragmenting high molecular mass N-acetylheparosan which is derived from the gene mentioned above. This gene comprises a DNA sequence encoding all or part of the peptide sequence SEQ ID N° 2.

Expression vectors characterized in that they carry, with the means necessary for the expression, the DNA fragment encoding the protein SEQ ID N° 2 capable of fragmenting N-acetylheparosan also form part of the invention.

To obtain the recombinant enzyme which is the subject of the present invention, the vector p466, which is described in detail in Patent Application EP-0,480,461, was used as vector.

However, it is also possible to use other expression vectors, for example those described by Studier FW and Moffatt BA in J. Mol. Biol (1986), 189, pp. 113-130 and to transform one of the recipient strains recommended by these authors.

The subject of the invention is also more particularly the plasmid p868,26. This plasmid was obtained by ligating a fragment of the plasmid p466 to a DNA fragment obtained after the polymerase chain reaction using an oligonucleotide whose sequence is the following: ##STR2## in the presence of an oligonucleotide whose sequence is the following: ##STR3## A=deoxyadenosine-5'-phosphoric acid C=deoxyguanosine-5'-phosphoric acid

G=deoxycytidine-5'-phosphoric acid

T=deoxythymidine-5'-phosphoric acid.

The subject of the invention is also a bacterial strain, the bacterial strain TP 2339 transformed with the plasmid p868,26. This strain makes it possible to obtain the recombinant enzyme which is the subject of the present invention both in soluble form and in membrane form.

In the wild-type Escherichia coli strain, the induction of the enzyme is dependent in a complex manner on the components of the culture medium. In contrast, the method of obtaining the recombinant enzyme, which is the subject of the present invention, makes it possible to dispense with the complex natural raw materials, in particular of animal origin. Indeed, the gene encoding the recombinant enzyme is placed under the control of an inducible promoter made functional simply by adding IPTG (isopropyl-β-D-thiogalactoside) at the time judged most appropriate for the desired aim. For example, the time chosen for the induction will be situated in the exponential phase of the culture, at half the predictable maximum biomass.

The techniques used for introducing a DNA fragment encoding an enzyme for fragmenting high molecular mass N-acetylheparosan into an expression vector permitting large quantities of this enzyme to be obtained, are techniques which are well known to persons skilled in the art. They are presented in detail in the book by Sambrook Fritsch and Maniatis "Molecular cloning: A Laboratory manual" published in 1989 by the publishers Cold Spring Harbor Press (N.Y.) 2nd edition.

The recombinant enzyme which is the subject of the present invention makes it possible to fragment N-acetylheparosan and to obtain fragments comprising, at the non-reducing end, a glucuronic acid residue having a double bond between carbons 4 and 5 (removal of the OH group). Such enzymes do not require water in the chemical reaction considered and are said to be of the eliminase type. The recombinant enzyme which is the subject of the present invention is therefore an eliminase and especially an endo-β-eliminase.

The recombinant enzyme which is the subject of the present invention can be used for fragmenting high molecular mass N-acetylheparosan either in its membrane form or in its soluble form.

The membrane form of the recombinant enzyme is present spontaneously in the bacterial pellet after centrifugation or filtration of the culture of the recombinant strain. An extraction of the pellet in the presence of Triton X-100 makes it possible to obtain the recombinant enzyme in soluble form. This extraction is made for example using an extraction buffer consisting of:

Tris.HCl 25 mM

NaCl 9 g/l

Triton X-100 30 g/l

(pH=7.0)

The bacterial pellet of the Escherichia coli strain recombinant enzyme is resuspended in the extraction buffer. After allowing to stand for 1 hour at room temperature, the culture suspension is centrifuged and the supernatant stored. The supernatant can be used as it is since the triton X-100 has no inhibitory effect on the enzyme.

The soluble form of the enzyme is also present spontaneously in the recombinant strain culture supernatant. It is therefore possible to isolate it from the supernatant by removing the bacteria from the culture by centrifugation or by microfiltration.

The soluble recombinant enzyme can be stored at the temperature of -20° C.

The term "preparation containing the enzyme" includes both the preparations containing the membrane form of the enzyme and the preparations containing the soluble form of the enzyme.

The preparations containing the recombinant enzyme in soluble form or in membrane form also form part of the invention. The various preparations containing the recombinant enzyme which is the subject of the present invention and especially the preparations containing the enzyme in membrane form or in soluble form are particularly useful for preparing low molecular mass N-acetylheparosans, for the following reasons:

the high molecular mass N-acetylheparosan is obtained in inexpensive synthetic medium with yields higher than those of a complex medium, a medium necessary for producing a small molecular mass N-acetylheparosan;

the high molecular mass N-acetylheparosan is technically easier to handle than that of small molecular mass;

the in vitro fragmentation separates the production phase from that of fragmentation, which makes it possible to control and optimize both phases while offering a wide scope in relation to the characteristics of the desired product, for example in relation to its molecular mass;

the recombinant enzyme and the high molecular mass N-acetylheparosan are particularly stable, which allows multiple recyclings which may be necessary in the implementation of dynamic processes, during which the fragmentation and fractionation processes are implemented simultaneously or successively while dispensing with the time constraints linked to the use of a bioreactor;

a recombinant strain, unlike the wild-type strain SEBR 3282 Escherichia coli (K5), makes it possible to fragment large quantities of high molecular mass N-acetylheparosan. Indeed, 1 liter of culture supernatant containing the recombinant enzyme is capable of fragmenting about 10-100 liters of N-acetylheparosan culture, which corresponds to 30-400 g of high molecular mass N-acetylheparosan.

To obtain a small molecular mass N-acetylheparosan having fragments corresponding to 9-10 disaccharide units, the soluble recombinant enzyme obtained spontaneously in the culture supernatant of the recombinant strain which is the subject of the present invention is preferably used. The final concentration of the high molecular mass N-acetylheparosan subjected to the action of the soluble enzyme is 2-30 g/l, more particularly 8-12 g/l, preferably 10 g/l.

The soluble enzyme is diluted such that a quantity of high molecular mass N-acetylheparosan 10-100%, preferably 50%, higher than that effectively used, which is 10 g/l, can be fragmented during a reaction lasting 2 hours to 48 hours, preferably 16 to 24 hours.

The enzymatic reaction is carried out preferably in the presence of sodium chloride at pH 7 and at 37° C., with gentle stirring. The reaction is sufficiently slow to permit monitoring of the fragmentation of the high molecular mass N-acetylheparosan. This monitoring is performed by evaluating the molecular mass of the fragmented N-acetylheparosan by exclusion HPLC.

To obtain N-acetylheparosan fragments of size less than 9-10 disaccharide units, several alternatives are possible and especially:

either the soluble enzyme is used in the presence of calcium ions in substantial concentration,

or the recombinant enzyme is used in membrane form,

or the duration of the enzymatic fragmentation reaction is increased,

or the concentration of the dilute enzyme used for fragmenting the high molecular mass N-acetylheparosan is increased.

As calcium salt, calcium chloride can be used. The concentration of calcium ions is of the order of 1-300 mM, preferably 100 mM.

With the aim of obtaining N-acetylheparosan fragments of size greater than 9-10 disaccharide units, a partial enzymatic reaction is simply carried out, for example by limiting its duration. In this case, the various forms of the recombinant enzyme (membrane or soluble) can be equally used.

To stop the enzymatic reaction, several means can be used and especially:

cold temperature up to 4° C., the activity of the recombinant enzyme is reduced,

heat since the N-acetylheparosan is resistant to a temperature of about 60° C. and that the enzyme is inactivated at this temperature,

basic pH: the recombinant enzyme and N-acetylheparosan are resistant to pH 11 but the activity of the enzyme in this pH zone is reduced or zero,

acidic pH, for example pH 4 or,

80% ethanol which inactivates the enzyme and precipitates N-acetylheparosan.

The invention also relates to processes for fragmenting a high molecular mass N-acetylheparosan using the recombinant enzyme which is the subject of the present invention.

For the implementation of the invention, the preparation of N-acetylheparosan predominantly of high molecular mass proved to be necessary. It does not form part of the invention but this preparation is also presented in detail below.

The production of the DNA fragment carrying the gene encoding the enzyme for fragmenting N-acetylheparosan and the adjacent sequences permitting its expression, its characterization as well as the various genetic engineering tools and processes which have permitted the production of the recombinant enzyme, are described in detail below in the different "sections".

An example of the use of the enzyme for fragmenting high molecular mass N-acetylheparosan illustrates the use of the recombinant enzyme which is the subject of the present invention.

It is given with no limitation being implied.

PREPARATION N-ACETYLHEPAROSAN OF PREDOMINANTLY HIGH MOLECULAR MASS

400 ml of the medium B, of a composition which is specified in Table I below, are inoculated with the strain SEBR 3282 of Escherichia coli (K5) deposited at the CNCM of the Pasteur Institute, Paris - France, under No. I-1013, and the mixture is incubated, with stirring, for 2 hours at 37° C. The preculture obtained is then transferred into an 18.5 liter fermenter containing 11 liters of the medium A, of a composition which is also specified in Table I below, and the mixture is incubated for 6 hours and 30 minutes at 37° C. and a pH equal to 7.2, the partial pressure of oxygen being maintained at 40 mmHg by regulating the injection of air (up to 20 l/minute) and the stirring. Glycerol is then added by continuously introducing a sterile solution containing 500 g/l of glycerol at the rate of 18 g/h for 16-17 hours.

The culture is continued under the same conditions of temperature, pH and partial pressure of oxygen until practically all the glycerol has been consumed. The monitoring of the optical density (OD) at λ=600 nm of the culture suspension at the end of the addition of glycerol, shows a stationary or slight lysis state until the culture is stopped at 28-30 hours old in the fermenter.

The culture suspension is then cooled to 25° C., centrifuged from 11,000 to 14,000 g for 15 to 20 minutes. The supernatant is supplemented with 0.1M NaOH (the pH increases to about 10) and again centrifuged. The resulting supernatant is then concentrated without delay in Amicon® hollow fiber cartridges with a 10 kD cut-off or equivalent, and then the solution is neutralized (pH=7). A solution enriched with high molecular mass N-acetylheparosan is thus obtained. An adequate quantity of sodium chloride is added to the solution in order to have a final NaCl concentration of 0.5 M, and then 4 volumes of ethanol are added. The precipitate is allowed to form overnight at 4° C. After a first removal of the supernatant by pumping, the precipitate is centrifuged at 5,000 g for 20 minutes at room temperature. The centrifugation pellets are taken up in ethanol, the suspension obtained is stirred and it is allowed to stand for 1 hour at room temperature. The centrifugation and suspending operations are repeated. A centrifugation is again carried out at 5,000 g for 20 minutes. The centrifugation pellets obtained are dried in a vacuum oven at 40° C. for 24 hours. The N-acetylheparosan thus obtained is a "purified high molecular mass N-acetylheparosan".

                  TABLE I                                                          ______________________________________                                         Composition and preparation of the medium A and the medium                     ______________________________________                                         B.                                                                             MEDIUM A                                                                       In 900 ml of ultra-purified water dissolved in order:                          Tricine ®N'[Tris-(hydroxymethyl)methyl]glycine)*                                                      360     mg                                          K.sub.2 HPO.sub.4          790     mg                                          Glutamic acid              11000   mg                                          MgCl.sub.2.6H.sub.2 O      500     mg                                          K.sub.2 SO.sub.4           450     mg                                          FeSO.sub.4.7H.sub.2 O      18      mg                                          CaCl.sub.2.2H.sub.2 O      2       mg                                          NaCl                       500     mg                                          KCl                        5000    mg                                          Solution of trace elements (cf. Table II)                                                                 1       ml                                          Glycerol                   10000   mg                                          Adjust the pH to 7.2 with concentrated potassium hydroxide of                  density 1.38 and fill to 1000 ml with ultra-purified water.                    Perform a degerminating filtration on a 0.2 μm membrane.                    Glycerol solution                                                              Dissolve 50 g of glycerol in a sufficient quantity of ultra-                   purified water and adjust the volume to 1000 ml with the same                  solvent. Perform a degerminating filtration on a 0.2 μm mem-                brane.                                                                         The antifoam used during the fermentation is Struktol J 673 ®              (Schill and Seilacher).                                                        MEDIUM B                                                                       The preparation of the medium B is identical to that of the                    medium A, the only difference being that it is advisable to add,               in addition, the buffer (pH 7.2): 3-morpholinopropane-sulphonic                acid (M.O.P.S.) after adding the antifoaming agent.                            ______________________________________                                          *(marketed by Fluka)                                                     

                  TABLE II                                                         ______________________________________                                         Preparation of the solution of trace elements                                  ______________________________________                                         in 800 ml of ultra-purified water dissolve (in order):                         H.sub.3 BO.sub.3           500     mg                                          Na.sub.2 MoO.sub.4.2H.sub.2 O                                                                             1930    mg                                          CoCl.sub.2.6H.sub.2 O      11850   mg                                          CuSO.sub.4.5H.sub.2 O      25      mg                                          ZnSO.sub.4.7H.sub.2 O      2000    mg                                          AlCl.sub.3.6H.sub.2 O      2410    mg                                          Add 100 ml of hydrochloric acid of density 1.9 and fill to 1000 ml             with ultra-purified water.                                                     ______________________________________                                    

SECTIONS 1-PREPARATION OF THE GENOMIC DNA OF THE STRAIN SEBR 3282 OF ESCHERICHIA COLI

A colony of the strain SEBR 3282 of Escherichia coli (K5) is cultured at 37° C. with stirring, in 5 ml of LB medium (Bactotryptone 5 g/l, yeast extract 10 g/l, NaCl 5 g/l: pH 7.35) overnight. One millimeter of this culture is used to inoculate a 1 liter flask containing 100 ml of the same culture medium and incubated at 37° C. on an orbital shaker set at 180 revolutions per minute. When the optical density of the culture, measured at X=600 nm, is equal to 1, the bacteria are centrifuged for a few minutes at 10000 rpm (Beckman J2.21) and taken up in 20 ml of a buffer of the following composition: 10 mM Tris-HCl pH 8.0, 20 mM EDTA, 0.1% SDS, 50 μg/ml proteinase K (Sigma® P 2308).

This bacterial suspension is incubated for 1 hour at 60° C. The enzymatic reaction is stopped by two phenol extractions (Appligene® ref. 130181) followed by extraction with dichloromethane. The nucleic acids are precipitated in the presence of 0.1M NaCl and two volumes of ethanol, and resolubilized in 10 ml of a TE buffer (10 mM Tris HCl, pH 8.0; 1 mM EDTA) containing 10 μg/ml of RNase (Boehringer Mannheim® 1119915).

After incubating for one hour at 37° C., the solution is again subjected to two phenol extractions followed by extraction with dichloromethane. The DNA obtained is precipitated in the presence of 0.1M of NaCl and two volumes of ethanol are then resolubilized with 10 ml of TE buffer. An aliquote fraction of this DNA, about 10 μg, is subjected to partial hydrolysis with the restriction enzyme SAU3A (Appligene®) under the conditions recommended by the supplier.

The partially hydrolysed DNA is subjected to electrophoresis on 1% agarose gel in the presence of the 1Kbp (kilo base pairs) size reference (BRL ref. 520-5615 SA). The DNA band which corresponds to a size of about 3 Kbp is purified by the geneclean technique (Bio 101® ref. 3105).

An aliquot fraction (approximately 200 ng) of the genomic DNA band, hydrolysed with SAU3A and whose size is about 3 Kbp, is ligated according to the technique described in "Molecular cloning: A Laboratory manual" (Sambrook, Fritsch and Maniatis, Cold Spring Harbor Press (N.Y.) 2nd edition (1989) pp. 1:63-1:67) in the presence of the vector pUC 18 hydrolysed with BamH1 and dephosphorylated (Pharmacia® Ref. 27-4855-01) in the appropriate reaction mixture described "Molecular cloning: A Laboratory manual" (document referenced above) overnight at 4° C.

This ligation mixture is used to transform, under the conditions recommended by the supplier, the strain RRI of Escherichia coli (K12) (GIBCO-BRL ref. 530-8261 SA). The result is a mixture called "transformation mixture" which is plated after dilution on 10 Petri dishes containing the LB medium previously described and supplemented with 15 g/l of noble agar and 100 mg/ml of ampicillin.

After incubating overnight at 37° C., the Petri dishes become covered with about 700 colonies each derived from a clone. Each Petri dish corresponds to one pool and the ten pools are classified from A to J and grouped under the number 838. Each clone has a DNA fragment of between 3 and 4 Kbp in size. The set of ten pools represents approximately 4 times the entire genome of Escherichia coli.

2-PURIFICATION OF THE CLONE 838,7 PRODUCING THE ENZYME INTENDED FOR FRAGMENTING N-ACETYLHEPAROSAN

The clone having an eliminase activity was detected by the fragmentation of high molecular mass N-acetylheparosan in vitro. The fragmentation of high molecular mass N-acetylheparosan was followed by analysis of the molecular mass of the fragmented N-acetylheparosan by exclusion HPLC.

2.1-Incubation of the pools of transformed bacteria

The preceding 10 pools formed by the transformation mixture described in Section 1, are plated in Petri dishes on agar LB medium (with agar) supplemented with 100 μg/ml of ampicillin and incubated for 48 hours at 37° C. The resulting bacterial lawn is resuspended in 3 ml of buffer A (of the following composition: 100 mM bis-Tris-propane; 150 mM NaCl, the pH is adjusted to 6.6 with hydrochloric acid). These bacterial suspensions are used to carry out the enzymatic fragmentation reaction.

2.2-Enzymatic fragmentation reaction

50 μl of a solution of high molecular mass N-acetylheparosan at 20 g/l are added to 500 μl of buffer A described above. To obtain this solution, a sufficient quantity of purified high molecular mass N-acetylheparosan (Preparation) is dissolved in ultra-purified water. The reaction mixture thus constituted is incubated from 3 to 4 days in an Eppendorf tube at 40° C.

2.3-Analysis of the fragmentation products

Preparation of the samples

The reaction mixture in an Eppendorf tube is then centrifuged at 10,000 g for 3 minutes. 100 μl of the supernatant are precipitated by adding 4 volumes of ethanol and then again centrifuged under the same conditions. The resulting pellet is taken up in 300 μl of 25 mM piperazine buffer, pH 3.5 (0.215 g of anhydrous piperazine are dissolved in 90 ml of ultra-purified water; the pH is adjusted to 3.5 with 1M HCl and then the volume is adjusted to 100 ml with ultra-purified water) and loaded onto a microcolumn prefilled with 100 μl of Q-Sepharose® resin. The washing of the microcolumn is performed with 2 ml of 25 mM piperazine buffer (pH 3.5) followed by 2 ml of ultra-purified water. The elution is performed with 200 μl of NaCl 0.5M. The eluate thus prepared is used directly for analysis by exclusion HPLC chromatography.

Operating conditions for exclusion HPLC

A 65 μl sample of this eluate containing the purified N-acetylheparosan is analysed by exclusion chromatography on an isocratic HPLC chain. The operating conditions are the following:

Column: TSK 2000 SW® (Toso-Haas) of 300×7.5 mm consisting of silica beads 1 μm in diameter and with a porosity of 125 Å.

Eluent: 0.5 M aqueous sodium sulphate solution, filtered on a 0.2 μm filter and degassed

Flow rate: 1 ml/min.

UV Detection: 205 nm

The calibration is performed by means of a range of oligosaccharides derived from heparin (10 mg) of the following molecular masses (Da): 3410, 4000, 4540, 5000, 6150, 7540, 10090.

Interpretation of the results

On the graphs obtained, the plot between the vertex of the peak corresponding to the high molecular mass species and the peak corresponding to the exit of sodium chloride is examined. If this line bends upwards compared with the control,--which reflects the presence of smaller sized N-acetylheparosan fragments--, this is considered as sign of a fragmentation activity and therefore of the presence of the desired enzyme in the pool which is the source of the reaction mixture.

2.4-Results

The pool I, among the 10 pools marked from A to J, was found to be positive and was used subsequently. An aliquote sample stored in glycerol at -80° C. was replated on a dish, and 1200 clones were obtained. These clones were analysed in tens and finally a producing clone called plasmid p838,7 was selected.

3-ANALYSIS OF THE PLASMID p838,7

The strain RRI of Escherichia coli (K12) transformed with the plasmid p838,7 is cultured in 500 ml of LB medium supplemented with 100 μg/ml of ampicillin. This strain has been deposited at the CNCM of the Pasteur Institute, Paris, France on 6th Aug. 1993, under the number I-1352.

The plasmid present in this strain is purified by the method of Qiagen® (Diagen® ref. 10.043). The plasmid called p838,7 is hydrolysed according to methods known to persons skilled in the art with several restriction enzymes: EcoRI, HindIII, Pstl, Sphl, Xbal, Sca1 (New England Biolabs Beverly Mass. 01915-5599 USA). Analysis of the restriction map obtained shows that the size of the DNA fragment obtained from the genomic DNA of the strain SEBR 3282 of Escherichia coli (K5) is about 3100 bp. The complete determination of the sequence is then carried out by the Sanger technique described in PNAS (1977), 74, pp. 5463-5467.

The complete nucleotide sequence of the DNA fragment carrying the gene encoding the enzyme for fragmenting high molecular mass N-acetylheparosan and the expression systems permitting its biosynthesis is the SEQ ID NO: 1 sequence.

4-ANALYSIS OF THE NUCLEOTIDE SEQUENCE OF THE DNA FRAGMENT CARRYING THE ENZYMATIC ACTIVITY

The DNA fragment of S₁ sequence, whose exact size is 3089 bp, carries the gene encoding the enzyme for fragmenting high molecular mass N-acetylheparosan but also the regulatory signals permitting its expression. Indeed, this fragment alone is capable of ensuring the production of the enzyme for fragmenting the high molecular mass N-acetylheparosan polysaccharide. These regulatory signals are in particular:

a -a specific promoter which is essential for the transcription of the gene.

b -a ribosome-binding site which is essential for carrying out the translation of the protein from the mRNA transcribed.

Computer analysis of the nucleotide sequence reveals several reading frames. A reading frame is an amino acid sequence deduced from the nucleotide sequence, via the genetic code, which starts with a methionine encoded by ATG, and which ends with one of the stop codons TAA, TGA or TAG (Sambrook, Fritsch and Maniatis, Cold Spring Harbor Press (N.Y.) 2nd edition (1989) pp. D1). Several possible reading frames exist in the SEQ ID NO: 1 sequence whose size is less than 100 amino acids. The latter will not be described.

There is also a reading frame whose size is 820 amino acids. FIG. 1 shows the double-stranded nucleotide sequence of the SEQ ID NO: 1 fragment from which the reading frame of 820 amino acids is derived.

The sequence of the longest reading frame whose size is 820 amino acids is the SEQ ID NO: 2 sequence. This sequence is compared with that of the proteins contained in data banks.

In this sequence, there can be observed:

a-The existence of a homology with an enzyme of the Erwinia chrysanthemi species possessing an exo-poly-α-D-galacturonidase activity. This enzyme is described in J. Bacteriol. (1990), 172, pp. 4988-4995 and PNAS (1992), 83, pp. 8990-8994. The first document describes its sequence in detail.

b-The repetition of the sequence <<asparagine (Asn)-A-B-serine(Ser)>>, where A is isoleucine (Ile), leucine (Leu) or tyrosine (Tyr) and B valine (Val), isoleucine (Ile) or alanine (Ala), at positions 384-387,411-414, 433-436, 461-464, and 495-498. One of its sequences <<Asn-Ile-Ala-Ser>> in position 461-464 is part of a potential site of attachment of lipoproteins to lipids. This binding sequence is known in the literature (Hayashi S., Wu H. C. J. in Bioenerg. Biomembr., (1990), 22., pp. 451-471; Klein P., Somorjai R. L. Lau P. C. K., Protein Eng., (1988), 2, pp. 15-20; von Heijne G. in Protein Eng., (1989), 2, pp. 531-534; Mc Gavin M. J., Forsberg C. W., Crosby B., Bell A. W., Dignard D., Thomas D. Y. in J. Bacteriol. (1989), 171, pp. 5587-5595; Rothe B., Roggentio P., Frank R., Bloecker H., Schauer R., in J. Gen. Microbiol. (1989), 135, pp. 3087-3096).

According to a computer program contained in "UWGCG" (University Wiscousin Genetic Computer Group-University Research Park 575 Science Drive Suite B, Madisson Wis. 53711), a potential site for binding to lipids could be <<Asn Ile Ala Ser Asn Ile Leu Met Thr Gly Cys>>.

c-The presence of a highly positively charged sequence at the C-terminal end of the peptide sequence. It is the sequence <<Arg Arg Arg Val Lys Lys>> which is positioned at amino acids 804-809.

5-EXPRESSION OF VARIOUS FORMS OF THE GENE IN ESCHERICHIA COLI (K12)

Without additional experiment, neither the localization of the promoter responsible for the transcription of the gene nor the beginning of the messenger RNA encoding the protein can be determined with certainty. Consequently, it was chosen to express the proteins which start with a methionine, itself preceded by a ribosome-binding site also called Shine-Dalgarno sequence. The ribosome-binding site in Escherichia coli (K12) is described in the literature (PNAS (1974), 71 No. 4, pp. 1342-1346 and Nucleic Acid Research (1982), 10 No. 9, pp. 2971-2996).

The methionines which are preceded by a potential site for binding to the ribosomes are four in number and Table III shows their positions in the peptide sequence SEQ ID NO: 2 and the nucleotide sequences SEQ ID NO: 1.

                  TABLE III                                                        ______________________________________                                                        SEQUENCES                                                       METHIONINE POSITION                                                                             PEPTIDE   NUCLEOTIDE                                          ______________________________________                                         methionine 1      1        310-311-312                                         methionine 2     112       642-643-644                                         methionine 3     160       787-788-789                                         methionine 4     194       888-889-890                                         ______________________________________                                    

5.1-Cloning into a vector for expressing the four proteins

A-Description of the polymerase chain reaction technique

The polymerase chain reaction (PCR) technique is a well known method which makes it possible to simultaneously copy the previously denatured strands for a DNA sequence using two oligonucleotides as primer [H. A. Erlich, "PCR Technology: Principles and Applications for DNA amplification", (1989), Ed. Macmillan Publishers Ltd, UK, and M. A. Innis et al., "PCR Protocols", (1990), Ed. Academic Press Inc San Diego, Calif. 92101, USA]. The principle of this technique is summarized below.

Numerous cycles, each of which consists of three stages, cause the amplification of the DNA strands of interest; the three stages are:

a) denaturation of the template

b) annealing of the primers to the template

c) extension of the primers.

After a few hours of cycles, hundreds of thousands of copies of the original template were produced by means of a thermostable DNA polymerase of Thermus aquaticus, usually called Taq polymerase. The PCR technique is based on the repetition of the three stages mentioned above.

a) Denaturation of the template:

Double-stranded DNA is denatured into single-stranded DNA by incubating at high temperature (92° C.-96° C.) for approximately 2 minutes.

b) Annealing of the primers:

These primers are a pair of synthetic oligonucleotides which anneal to the ends of the region to be amplified. The two primers anneal to opposite strands. The primers are added in excess so that the formation of the primer-template complex is favoured.

c) Extension of the primers:

The stage during which Taq polymerase brings about the extension of the primer-template complex from 5' to 3' is carried out at 72° C.

In the PCR technique, the product of interest appears during the third cycle and it is then amplified substantially. During the progress of the cycles, the amplification product rapidly becomes the major template to which the primers become annealed.

B -Description of the primers used

5 synthetic oligonucleotides were prepared from the sequence of FIG. 1. The first oligonucleotide, called primer 1, whose sequence is the following (SEQ ID N° 3): ##STR4## has two distinct regions. Region 1 is that which carries a cloning site CATATG corresponding to the endonuclease NdeI recognition site and region 2 that intended to become annealed to the 5' end of the gene encoding the protein starting with methionine 1.

The second oligonucleotide is the primer 2 whose sequence is the following (SEQ ID N° 4): ##STR5## has two distinct regions. Region 1 is that which carries a cloning site CATATG corresponding to the endonuclease NdeI recognition site and region 2 which is intended to become annealed to the 5' end of the gene encoding the protein starting with methionine 2.

The third oligonucleotide constituting primer 3, whose sequence is the following (SEQ ID N° 5): ##STR6## has two distinct regions. Region 1 which carries a cloning site CATATG corresponding to the endonuclease NdeI recognition site and region 2 which is intended to become annealed to the 5' end of the gene encoding the protein starting with methionine 3.

The fourth oligonucleotide constitutes primer 4, whose sequence is the following (SEQ ID N° 6): ##STR7## has two distinct regions. Region 1 is that which carries a cloning site CATATG corresponding to the endonuclease NdeI recognition site and region 2 intended to become annealed to the 3' end of the gene encoding the protein starting with methionine 4.

The fifth oligonucleotide called primer 5 whose sequence is the following (SEQ ID N° 7): ##STR8## has two distinct regions. Region 1 is that which carries a cloning site AAGCTT corresponding to the endonuclease HindIII recognition site and region 2 intended to become annealed to the 3' end of the gene encoding the protein.

5.2-Production of four amplified fragments corresponding to the four proteins

200 ng of the plasmid p838,7 hydrolysed with the restriction enzyme EcoRI (NEB) under the conditions recommended by the supplier, are mixed with:

100 ng of primer 1, 2, 3 or 4

100 ng of primer 5

200 μmol of each of the four deoxynucleotide triphosphates (adenosine, thymidine, cytidine, guanosine)

5 μl of reaction mixture concentrated ten fold (final concentration 67 mM Tris-HCl, pH 8.8, 16.6 mM (NH₄)₂ SO₄, 1 mM β-mercaptophenol (6.7 mM EDTA, 0.15% Triton®, 200 mg of gelatin).

The volume is then adjusted to 50 μl by adding water.

0.5 μl, equivalent to 2.5 units of Taq polymerase (Beckman® ref. 267301) is then added. After homogenizing the solution, the reaction mixture is covered with paraffin oil in order to avoid evaporation of the aqueous solution during the polymerase chain reaction.

The amplification is performed over 18 reaction cycles of which the stages of a cycle are the following:

1 minute at 92° C.→denaturation

1 minute at 55° C.→annealing

3 minutes at 72° C.→polymerization

After the 18 expected cycles, the enzymatic reaction is stopped by adding 20 mM EDTA.

The DNA fragments thus amplified have the expected sizes, which are the following:

primer 1: about 2460 bp

primer 2: about 2130 bp

primer 3: about 2000 bp

primer 4: about 1880 bp

These fragments are then isolated and purified on 1% agarose gel and then hydrolysed simultaneously with the enzymes NdeI and HindIII according to the recommendations of the supplier (New England Biolabs®) in order to form the NdeI and HindIII cohesive ends. After hydrolysis, the fragment is purified on an exclusion chromatography column.

5.3-Construction of the plasmids p868,26-p869,3-p886,3 and p887,7

This is the construction of the vectors for expressing the proteins whose corresponding peptide sequences start with the four potentially initial methionines described in Table III.

These four plasmids are prepared from the plasmid p466 corresponding to a vector for the cloning and expression of the complementary DNA, for Aspergillus flavus urate oxydase in Escherichia coli, described in Patent Appliction EP-0,408,461, which comprises a fragment of the plasmid pBR327 including the replication origin and the ampicillin-resistance gene, a synthetic Escherichia coli promoter, a Shine-Dalgarno sequence, followed by the gene encoding Aspergillus flavus urate oxydase flanked by the sequences recognized by the enzymes NdeI and HindIII, a transcriptional terminator (derived from the fd phage) and the lac i gene.

The plasmid p466 is hydrolysed according to the conditions recommended by the supplier with the enzymes NdeI and HindIII, and the fragment carrying the lac i gene, the fragment of the plasmid pBR327, the synthetic promoter, the Shine-Dalgarno sequence and the terminator is purified.

This fragment was ligated to each of the four fragments obtained after the polymerase chain reaction with the primers 1, 2, 3 and 4 in the presence of the primer 5 previously hydrolysed with the restriction endonucleases NdeI and HindIII in order to liberate the ends of these two sites, as described above (5.2). The product of these ligations was used to transform the strain RRI of Escherichia coli (K12) (GIBCO-BRL ref. 530-8261SA). The transformants obtained are analysed.

Table IV shows the transformants selected, corresponding to the various primers used in accordance with Table III, and Section 5.1, "B-description of the primers used".

                  TABIE IV                                                         ______________________________________                                                      CLONE  PLASMID                                                    ______________________________________                                         PRIMER 1        868,26   p868,26                                               PRIMER 2       886,3    p886,3                                                 PRIMER 3       887,7    p887,7                                                 PRIMER 4       869,3    p869,3                                                 ______________________________________                                    

5.4-Analysis of the protein produced by each of the four clones

The general scheme for studying the expression in these four vectors was the following:

A colony is used to inoculate a test tube prefilled with LB medium supplemented with 100 μg/ml ampicillin. The test tube is then kept stirring overnight at 37° C.

From this preculture, a flask prefilled with the same LB medium is inoculated 1/100 and the incubation is continued under the same conditions. After culturing for one hour, the induction is caused by the addition of 1 mM IPTG (Sigma® I-9003) and the incubation is continued for 3 hours or 24 hours, still under the same temperature and stirring conditions. The cultures, after expression, are subjected to various manipulations:

a) Preparation of the bacterial pellets whose cell density corresponds to 0.2 ml at OD=1 (λ=600 nm) for analysis on SDS-PAGE 10% acrylamide or 1 ml OD=3 for biochemical assay of the eliminase activity.

b) Separation supernatant/bacterial pellet by centrifugation at 10000 revolutions/minute for 5 minutes at 4° C.

c) Osmotic shock. Osmotic shock is a technique commonly used for extracting the proteins contained in the periplasm of Gram-negative bacteria. This technique consists in causing bacteria to pass from a medium at high osmotic pressure into a medium at low osmotic pressure. For example Neu et al. in J. Biol. Chem., (1965) 240, pp. 3685-3692 recommend the use of a concentrated sucrose solution containing EDTA as medium at high osmotic pressure and water as medium at low osmotic pressure. In some specific cases, cytoplasmic enzymes which might be localized on the inner face of the cytoplasmic membrane could also be extracted by-this process Int. J. Biochem. (1979), 10, pp. 877-883).

Table V summarizes the results obtained on the various constructions.

                  TABLE V                                                          ______________________________________                                                                              Activity                                  Methionine         Activity Activity osmotic                                   in position                                                                             Plasmid   pellet   supernatant                                                                             shock                                     ______________________________________                                          1        p868,26  +        +        +                                         112      p886,3    +        +        +                                         160      p887,7    +        -        not tested                                194      p869,3    +        -        not tested                                ______________________________________                                    

The plasmid p868,26, which produces in sufficient quantities the fragmentation enzyme in soluble form in the culture supernatant, is of specific interest for the production of fragments of predominantly 9-10 disaccharides.

5.5-Transformation of the plasmids p868,26 and p886,3 in the strains MC 1061 and TP 2339

The bacterial strain MC 1061 is described in J. Bacteriol. (1980), 143, No. 2, pp. 971-980, and the strain TP 2339 in U.S. Pat. No. 4,945,047.

Both bacterial strains were each transformed with the two plasmids p868,26 and p886,3 by the technique described in FMS (Sambrook Fritsch and Maniatis "Molecular cloning: A Laboratory manual" (1989), Ed. Cold Spring Harbor Press (N.Y.) 2nd edition pp. 1:75). Both transformed strains were cultured according to the method indicated above (5.4-analysis of the protein produced by each of the four clones). The bacterial pellets, the culture supernatants and the osmotic shock were assayed for their eliminase activity in the following manner:

the collected samples were diluted according to a series, and to each 125 μl of each dilution performed in the buffer A (described in 2.1-Incubation of the pools of transformed bacteria) are added 125 μl of high molecular mass N-acetylheparosan at the concentration of 20 g/l. The incubation is for 24 hours and the analysis of the fragments obtained is carried out according to the procedure described above (2.3-Analysis of the fragmentation products--Operating conditions for exclusion HPLC).

The results obtained are indicated in Table VI:

                                      TABLE VI                                     __________________________________________________________________________              PELLET   SUPERNATANT                                                                              OSMOTIC SHOCK                                               3 hours                                                                            24 hours                                                                            3 hours                                                                             24 hours                                                                            3 hours                                                                             24 hours                                      __________________________________________________________________________     p868,26/MC 1061                                                                         ND* ND*  ND*  ND*  ND*  +                                             p868,26/TP2339                                                                          ++  +    ND*  +++  ++   ND*                                           p886,3/MC1061                                                                           (+) ND*  ND*  ND*  +    (+)                                           p886,3/TP2339                                                                           ND* ND*  ND*  ND*  ND*  ND*                                           __________________________________________________________________________      ND* = not detectable                                                     

In this table, it is observed that the strain TP 2339 transformed by the plasmid p868,26 (p868,26/TP2339) after incubating for 24 hours has a high activity in the culture supernatant.

6-PRODUCTION OF THE SOLUBLE RECOMBINANT ENZYME 6.1-Culture

To obtain the soluble recombinant enzyme, a culture of the recipient strain TP 2339, which is a strain RRI of Escherichia coli (K12) transformed by the plasmid p868,26, is performed under environmental conditions which are favourable to the formation of the enzyme.

The recombinant strain is stored in a 20% glycerol tube at the temperature of -80° C. The medium used is the C medium which is indicated in Table VII, the only difference being that yeast extract is added at the rate of 2 g/l initially and 10 g/l after 7 hours of culture. The fermenter used is an 18 liter MBR fermenter equipped with oxygen pressure, temperature and pH regulators and the like.

Preculture

A tube of feed batch at -80° C. is thawed and 100 μl are collected and diluted 50 fold and then inoculated into a bottle with a low tube prefilled with 500 ml of LB medium. The bottle, containing a magnetic bar, is placed in a bath thermostatted at 30° C. and then connected to the fermenter to be inoculated via a hollow needle sterilely implanted in a septum. The plastic tube is inserted in a peristaltic pump and connected to a programmer. Following experiments and calculations, this scheme is convenient for inoculating a fermenter with an initial useful volume of 10 liters designed to start 11 hours after inoculating the bottle (for example, inoculation of the bottle started at 17 hours for inoculation of the fermenter at 4 o'clock in the morning).

Culture

The culture parameters are the following:

pH 7.4

Oxygen pressure: 40 mmHg regulated by stirring.

Temperature: 37° C.

Excessive pressure 0.1 bar at the top of the fermenter.

Other reagents used during the culture are the following:

H₂ SO₄ 3N consumption about 400 ml

KOH 3N consumption about 1200 ml

Antifoaming agent: Struktol® (Schill and Seilacher) type J 673®pure 50 ml.

A continuous supply of glucose is adjusted so as to provide a glucose concentration of between 10 and 20 g/l. The quantity of glucose consumed comprising the initial glucose of the medium is 1160 g.

The optical density of the solution measured at λ=600 nm reached the maximum of its value at a culture age of 11 hours, the biomass is then about 38 g/l.

Treatment of the culture suspension

The suspension is vigorously centrifuged at 14000 g in pots. The supernatant contains the soluble recombinant enzyme. The supernatant can be directly used, after suitable dilution, to fragment the high molecular mass N-acetylheparosan. The supernatant can also be stored by freezing at -20° C.

6.2-Assay of the eliminase activity

The detection of the activity of the recombinant soluble eliminase was performed by the fragmentation caused by a quantity of high molecular mass N-acetylheparosan.

150 μl of purified high molecular mass N-acetylheparosan (Preparation) at 20 g/l, solubilized in pH 7.0 buffer, were used as substrate. (For the preparation of this buffer, dissolve 100 mmol of bis-Tris-propane and 200 mmol of NaCl in water, and adjust the pH to 7 with concentrated HCl and fill to 1 liter).

150 μl supernatant containing the soluble recombinant enzyme obtained as indicated above (6.1-Treatment of the culture suspension), at various dilutions performed in pH 7.0 buffer were added to this substrate. This mixture is homogenized by stirring and then incubated at 37° C. with stirring in a rotary shaker at 300 rpm.

The reading is performed after incubating for 24 hours and the measurement is expressed in eliminase unit (E.U.). One eliminase unit is defined as the quantity of activity necessary to fragment 0.1 mg of high molecular mass N-acetylheparosan at the concentration of 10 g/l into N-acetylheparosan of small molecular mass equal to 5000 Da, in 24 hours, at 37° C., at pH 7.0 in the presence of added 200 mM NaCl.

The analysis of the fragmented N-acetylheparosan is carried out by exclusion HPLC according to the conditions described in Section 2 (2.3-Analysis of the fragmentation products).

Calculations

The soluble recombinant enzyme in the volume V (μl) diluted by a factor d_(E) at an OD equal to 1 at λ=600 nm (this optical density for Escherichia coli (K5) corresponds to a biomass of 400 mg/l) at the end of culture OD_(E) makes it possible to fragment the quantity Q_(K5) (mg) of high molecular mass N-acetylheparosan.

The specific activity (A_(SD)) at the end of the culture of the soluble recombinant enzyme is obtained by the formula: ##EQU1## which gives EU values/ml at OD=1.

The eliminase activity of the soluble recombinant enzyme described above (6.1) is 10 E.U.

                  TABLE VII                                                        ______________________________________                                         Composition and preparation of the medium C                                    MEDIUM C                                                                       ______________________________________                                         Medium C is prepared by combining the three sterile solutions                  below:                                                                         Solution No. 1                                                                 In 700 ml of ultra-purified water dissolve in order:                           Complexing agent: N'[Tris-(hydroxymethyl)methyl]                                                          360     mg                                          glycine (Tricine marketed by Fluka ®                                       FeSO.sub.4.7H.sub.2 O      280     mg                                          CaCl.sub.2.2H.sub.2 O      6.7     mg                                          MgCl.sub.2.6H.sub.2 O      1270    mg                                          K.sub.2 SO.sub.4           8710    mg                                          NaCl                       500     mg                                          KCl                        5000    mg                                          Casein hydrolysate (main source of amino acids)                                                           25000   mg                                          HY CASE SF ® (marketed by Sheffield)                                       Yeast extract (marketed by Difco ®)                                                                   18000   mg                                          Solution of trace elements (cf. Table II)                                                                 1       ml                                          Antifoaming agent Struktol J673 ® (marketed by Schill and                  Seilacher): a few drops using a Pasteur pipette.                               Adjust the pH to 7.4 with a KOH solution (d = 1.38) and fill to                850 ml with ultra-purified water. Autoclave the medium for 45                  minutes at 120° C.                                                      Solution No. 2                                                                 In about 40 ml of ultra-purified water, dissolve 5 g of                        K.sub.2 HPO.sub.4                                                              and then adjust to 50 ml with the same solvent. Filter the solution            obtained through a filter with a porosity of 0.2 μm.                        Solution No. 3                                                                 Dissolve 20.7 g of glucose in a sufficient quantity of ultra-                  purified water and adjust the volume to 100 ml with the same                   solvent. Autoclave at 110° C. for 30 minutes.                           ______________________________________                                    

7-AMINO-TERMINAL SEQUENCE OF THE RECOMBINANT ENZYME

The strain RRI of Escherichia coli (K12) was transformed with the plasmid 868,26 and cultured as described above (6. Production of the soluble recombinant enzyme; 6.1 Culture).

The bacterial pellet recovered by centrifugation was placed for one hour in contact with a solution of Triton X-100 in order to extract the recombinant enzyme therefrom in a soluble form.

After two purification steps by anion exchange chromatography on DEAE Sepharose Fast Flow® and gel filtration on Superdex 200® (Pharmacia), a pool having the following characteristics was obtained:

0.26 mg/ml of total proteins

eliminase activity on high MW N-acetylheparosan

predominant band of about 70,000 Da in SDS PAGE

This pool was dispatched for sequencing.

The sample of presumed recombinant enzyme was again loaded on a 10% SDS PAGE gel. The proteins were transferred onto Problot® membrane (Applied Biosystems) and stained with Coomassie blue. A doublet with a molecular mass close to 70,000 Da was detected.

The bands were loaded separately in an Applied Biosystems model 476 A sequencer. These two bands have the same amino-terminal sequence starting at threonine 2 (Thr2) residue of the theoretical peptide sequence SEQ ID NO: 2 of the recombinant enzyme.

The results obtained using an FSTNML program are given in Tables VIII and IX.

                  TABLE VIII                                                       ______________________________________                                         Band No. 1 - SEQUENCE NUMBER: 112                                              Sequence cycles                                                                            HPLC***    Identification                                                                            Conclusion                                   ______________________________________                                         PTH-AA* No. 1   Thr        11   pm**  Thr                                              No. 2   Val        20   pm    Val                                              No. 3   Ser        4    pm    Ser                                              No. 4   Thr        6    pm    Thr                                              No. 5   Glu        6    pm    Glu                                              No. 6   Val        13   pm    Val                                              No. 7   Asp        5    pm    Asp                                      ______________________________________                                    

                  TABLE IX                                                         ______________________________________                                         SEQUENCE NUMBER: 113                                                           Sequence cycles                                                                            HPLC***    Identification                                                                            Conclusion                                   ______________________________________                                         PTH-AA* No. 1   Thr        30   pm**  Thr                                              No. 2   Val        39   pm    Val                                              No. 3   Ser        33   pm    Ser                                              No. 4   Thr        14   pm    Thr                                              No. 5   Glu        29   pm    Glu                                              No. 6   Val        23   pm    Val                                              No. 7   Asp        22   pm    Asp                                              No. 8   His        10   pm    His                                              No. 9   Asn        29   pm    Asn                                              No. 10  Glu        15   pm    Glu                                      ______________________________________                                          *PTH-AA = phenylthiohydantoin                                                  **pm = picomolar                                                               ***HPLC chromatographic conditions: reversedphase chromatography; PTH C18      ® column: (Biosystems); elution solvent gradient of (A) and (B):           (A) = 30 mM acetate buffer in a 3.5% tetrahydrofuran solution (pH = 4) (B      = pure acetonitrile, gradient: 0-10 min B = 10%, 10-18 min B = 35-38%,         18-23 min B = 90%; flow rate = 0.3 ml/min; UV detection λ = 260 nm                                                                               

The amino-terminal sequence of the purified recombinant enzyme produced by the strain RRI of Escherichia coli (K12) transformed by the plasmid 868,26 corresponds to the beginning of the peptide sequence SEQ ID NO: 2 with the exception of amino-terminal formylmethionine. This amino acid was removed by an aminopeptidase (Waller J. P., J. Mol.Biol., (1963), 7, p483-496).

EXAMPLES

EXAMPLE 1

Fragmentation of high molecular mass N-acetylheparosan with the recombinant enzyme--production of an N-acetylheparosan with a molecular mass about 5000 Da

3 solutions (solutions A, B, C) of high molecular mass N-acetylheparosan are prepared (Preparation) by dissolving 20 g of N-acetylheparosan in ultra-purified water so as to obtain, after adding the recombinant enzyme solution, a final N-acetylheparosan concentration of 10 g/l. The soluble recombinant enzyme is used as enzyme. The quantity of soluble recombinant enzyme is calculated so that potentially, 15 g of high molecular mass N-acetylheparosan can be completely fragmented in 24 hours. The enzymatic reaction is carried out at 37° C. at pH 7 and with gentle stirring in the presence of 200 mM NaCl. The duration of the reaction is about 15 hours. It is monitored by exclusion HPLC as described in section 2.3 (2.3-Analysis of the fragmentation products--Operating conditions for exclusion HPLC). The reaction is stopped by cooling. 3 batches of small molecular mass N-acetylheparosan are thus obtained, batches A, B and C.

The 3 batches of small molecular mass N-acetylheparosan which are obtained at the end of the reaction have a predominant peak which corresponds to 4800 Da evaluated relative to a standard reference consisting of a heparin fraction with a molecular mass of 4800 Da. The proportion of high molecular mass fragments is negligible or even zero at the end of the enzymatic reaction.

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 7                                                   (2) INFORMATION FOR SEQ ID NO: 1:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 3089 base pairs                                                    (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: double                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: DNA (genomic)                                              (iii) HYPOTHETICAL: NO                                                         (iii) ANTI-SENSE: NO                                                           (vi) ORIGINAL SOURCE:                                                          (A) ORGANISM: Escherichia coli                                                 (B) STRAIN: (K5) SEBR 3282                                                     (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1:                                       GATCCCGGAGTAATTTCATCAAGTGCGATCCCTCCACCAGTGACCTGACGCCTCCCGGCG60                 TGTGAATCCTTTCGGTAAATCCCTCTTCCAGTGG ATAGTGATACTGCTGCATCTTAATCT120               TCTCCATGCAATAACTGTATATTTATACAGTAGCAAATAATTTGTTTGCTATCCAGCACG180                TTTTGCAAATTACCTGAAAGGTAATATCTATTCATATTCACAGTCTTTCTATCCATATAT240                GGTTTTTTG GGTAATAGAATAACCAGATATGCGGCGCAACGGGTGCTGCGACTATCTGGA300               GATTTAACATGACGGTCTCAACCGAAGTTGACCACAACGAATACACAGGTAACGGCGTTA360                CGACATCATTTCCGTATACCTTCCGTATTTTCAAAAAATCCGACCTGGTTGT TCAGGTGT420               CTGACCTTAACGGTAACGTTACAAAACTAGTGCTGGATGCTGGTTATACGGTAACAGGGG480                CGGGAACTTATAGTGGCGGTGCAGTGGTTCTTCCGTCGCCGCTTGCTGCTGGCTGGCGAA540                TCACGATAGAGCGTGTGCTTGATGTGG TGCAGGAGACTGATCTTCGCAATCAGGGAAAAT600               TTTTCCCCGAAGTTCATGAGGATGCATTTGACTACCTGACGATGCTGATCCAGCGATGTT660                TTGGGTGGTTCAGACGTGCATTGATGAAACCATCTTTGCTTGCAAAATATTACGATGCAA720                A GCAAAACAGAATATCTAACCTTGCCGATCCATCACTTGAGCAGGACGCTGTAAATAATC780               GCTCAATGCGTAATTATGTCGATGCTGCAATCGCCGGAGTTATTGGTGGTTTTGGTTGGT840                TTATTCAGTATGGTTCTGGAGCGGTATACAGAACGTTCCAGGATA AGATGCGTGATGGTG900               TCAGCATTAAGGATTTTGGAGCTCAAAATGGAATCTTAAATGATAACAAGGATGCTTTTA960                CAAAATCATTACATTCGTTTAGCAGTGTTTTTGTTCCGGAAGGGGTATTCAATACATCTT1020               TAGTTTCTCTTTCACGTTGT GGCTTGTACGGAACAGGTGGGGGAACGATAAAACAGTATG1080              ACAGAGATGGTAATCATCTGGTTTTTAACATGCCCGATGGTGGCATGCTTAGTACGCTAA1140               CAATTATGGGAAATAAATCAGATGATAGTGTGCAGGGACACCAGGTGTCATTTTCAGGTG1 200              GCCATGATGTATCGGTTAAAAATATCAGATTTACAAATACGCGAGGACCAGGATTTAGCT1260               TGATCGCTTATCCGGATAATGGTATTCCGTCAGGTTACATTGTTAGAGATATAAGAGGAG1320               AGTATTTAGGGTTCGCAAATAATAAAAAAGCAGGTTGT GTGCTTTTTGATTCATCGCAAA1380              ATACGCTAATTGATGGTGTGATAGCCAGAAATTATCCTCAGTTTGGTGCAGTGGAACTTA1440               AAACAGCAGCAAAATATAACATTGTCAGCAATGTTATTGGTGAAGAGTGTCAGCACGTTG1500               TTTACAATGGAA CTGAGACGGAAACTGCCCCAACGAATAATATCATTAGCAGTGTAATGG1560              CTAACAACCCAAAATACGCCGCAGTAGTTGTTGGCAAGGGGACTGGTAACCTGATTTCGG1620               ATGTGCTGGTTGATTACTCTGAATCGGACGCAAAGCAGGCGCACGGCGTCACCGTT CAGG1680              GAAATAATAATATTGCCAGTAATATTCTAATGACTGGGTGTGATGGGAAAAATGAATCAG1740               GAGATCTGCAGACATCTACAACCATTCGTTTCTTAGATGCTGCACGCAGTAATTATGCGT1800               CAATATTCCCCATGTATAGTTCTTCCGGCG TGGTTACCTTCGAGGAAGGGTGTATCAGGA1860              ACTTTGTTGAAATTAAACATCCGGGTGACAGAAATAATATTCTGAGTTCTGCATCAGCGG1920               TGACTGGTATTTCCAGTATAGACGGCACTACAAATAGCAATGTTGTTCACGTCCCTGCGC1980               TTGGT CAGTACGTTGGGACTATGTCAGGGCGTTTTGAATGGTGGGTTAAATATTTTAACC2040              TTGCTAACCAGACGCTTGTTTCTGCAGATAAATTCAGAATGCTTGCTGAAGGCGATGTAT2100               CTCTGGCTGTGGGAGGCGGTATAAGTTCGCAATTGAAATTATTCAATAG TGATAATACTA2160              AAGGCACTATGTCGCTAATAAATGGAAATATTCGAATATCTACTGGAAATTCAGAATATA2220               TACAGTTTTCTGATTCAGCCATGACACCATCGACAACGAATACTTATTCTCTTGGGTTGG2280               CTGGTCGTGCATGGTCGGGGGGA TTTACCCAGTCAGCGTTTACGGTGCTGTCCGATGCGC2340              GTTTCAAGACTGCTCCAGAGGTTATTGATGAGAAAATACTGGACGCATGGGAAAGAGTGG2400               AATGGGTTTCATACCAGTACCTTGACAGGATCGAAGTGAAAGGTAAAGACGGAGCAAGAT2460               GGCACTTTGGTGCAGTTGCGCAGCATGTTATCAGTGTATTTCAGAATGAAGGCATAGATG2520               TGTCACGACTGGCATTTATCTGTTATGACAAGTGGAATGAGACCCCGGCAGAATACAGGG2580               ATGTGACGGAAGAAGAGCATTCTGCAGGAGTTTACCCACTT ATACAGACAAAGGTTCTGG2640              TACGCGAAGCCGTCGAGGCTGGTGAATGTTACGGTATCCGTTATGAAGAGGCTCTGATTC2700               TGGAATCTGCGATGATGAGACGCAGGGTTAAAAAGCTGGAAGAGCAAGTTTTGCAATTAA2760               CAGGGAATTGAACCGT AAATGGTGTGTTGTTGCGCGGTATACTTTTCCTGAAGCAGGGTG2820              TTTGCAAATAAACGGGTTTCGTTATGTCATTCCAACTAACCAATGAAACTTCAAATCAGT2880               GGCTTAGTGTTAGTTCTCTTGCTGCGGTTATTGCAGGTGTCCCTCCGGAGGTTGCTTTGG 2940              GGGCTTTGGCTGGGGCGGTAATTTTTGTTACCTCTGCGGTAGAGTATCCTATTCGTCGTC3000               GTGTACTCTTGTCGATGCTTAGCTTTCTCTGCGGCCTTCTTTTTTATAAACCAGCAGCAT3060               CAATTCTTATCGGCATAGCCAGCCTGATC 3089                                             (2) INFORMATION FOR SEQ ID NO: 2:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 820 amino acids                                                    (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 2:                                       MetThrValSerThr GluValAspHisAsnGluTyrThrGlyAsnGly                              151015                                                                         ValThrThrSerPheProTyrThrPheArgIlePheLysLysSerAsp                                202530                                                                        LeuValValGlnValSerAspLeuAsnGlyAsnValThrLysLeuVal                               354045                                                                         LeuAspAlaGlyTy rThrValThrGlyAlaGlyThrTyrSerGlyGly                              505560                                                                         AlaValValLeuProSerProLeuAlaAlaGlyTrpArgIleThrIle                               657 07580                                                                      GluArgValLeuAspValValGlnGluThrAspLeuArgAsnGlnGly                               859095                                                                         LysPhePhe ProGluValHisGluAspAlaPheAspTyrLeuThrMet                              100105110                                                                      LeuIleGlnArgCysPheGlyTrpPheArgArgAlaLeuMetLysPro                                115120125                                                                     SerLeuLeuAlaLysTyrTyrAspAlaLysGlnAsnArgIleSerAsn                               130135140                                                                      LeuAlaAspProSer LeuGluGlnAspAlaValAsnAsnArgSerMet                              145150155160                                                                   ArgAsnTyrValAspAlaAlaIleAlaGlyValIleGlyGlyPheGly                                165170175                                                                     TrpPheIleGlnTyrGlySerGlyAlaValTyrArgThrPheGlnAsp                               180185190                                                                      Ly sMetArgAspGlyValSerIleLysAspPheGlyAlaGlnAsnGly                              195200205                                                                      IleLeuAsnAspAsnLysAspAlaPheThrLysSerLeuHisSerPhe                                210215220                                                                     SerSerValPheValProGluGlyValPheAsnThrSerLeuValSer                               225230235240                                                                   L euSerArgCysGlyLeuTyrGlyThrGlyGlyGlyThrIleLysGln                              245250255                                                                      TyrAspArgAspGlyAsnHisLeuValPheAsnMetProAspGlyGl y                              260265270                                                                      MetLeuSerThrLeuThrIleMetGlyAsnLysSerAspAspSerVal                               275280285                                                                       GlnGlyHisGlnValSerPheSerGlyGlyHisAspValSerValLys                              290295300                                                                      AsnIleArgPheThrAsnThrArgGlyProGlyPheSerLeuIleAla                                305310315320                                                                  TyrProAspAsnGlyIleProSerGlyTyrIleValArgAspIleArg                               325330 335                                                                     GlyGluTyrLeuGlyPheAlaAsnAsnLysLysAlaGlyCysValLeu                               340345350                                                                      PheAspSerSerGlnAsnThrLeuIleAspGlyValIle AlaArgAsn                              355360365                                                                      TyrProGlnPheGlyAlaValGluLeuLysThrAlaAlaLysTyrAsn                               370375380                                                                       IleValSerAsnValIleGlyGluGluCysGlnHisValValTyrAsn                              385390395400                                                                   GlyThrGluThrGluThrAlaProThrAsnAsnIleIle SerSerVal                              405410415                                                                      MetAlaAsnAsnProLysTyrAlaAlaValValValGlyLysGlyThr                               420425 430                                                                     GlyAsnLeuIleSerAspValLeuValAspTyrSerGluSerAspAla                               435440445                                                                      LysGlnAlaHisGlyValThrValGlnGlyAsnAs nAsnIleAlaSer                              450455460                                                                      AsnIleLeuMetThrGlyCysAspGlyLysAsnGluSerGlyAspLeu                               465470475 480                                                                  GlnThrSerThrThrIleArgPheLeuAspAlaAlaArgSerAsnTyr                               485490495                                                                      AlaSerIlePheProMetTyrSerSerS erGlyValValThrPheGlu                              500505510                                                                      GluGlyCysIleArgAsnPheValGluIleLysHisProGlyAspArg                               515520 525                                                                     AsnAsnIleLeuSerSerAlaSerAlaValThrGlyIleSerSerIle                               530535540                                                                      AspGlyThrThrAsnSerAsnValValHisVal ProAlaLeuGlyGln                              545550555560                                                                   TyrValGlyThrMetSerGlyArgPheGluTrpTrpValLysTyrPhe                               565 570575                                                                     AsnLeuAlaAsnGlnThrLeuValSerAlaAspLysPheArgMetLeu                               580585590                                                                      AlaGluGlyAspValSerLeu AlaValGlyGlyGlyIleSerSerGln                              595600605                                                                      LeuLysLeuPheAsnSerAspAsnThrLysGlyThrMetSerLeuIle                               6106 15620                                                                     AsnGlyAsnIleArgIleSerThrGlyAsnSerGluTyrIleGlnPhe                               625630635640                                                                   SerAspSerAlaMetThrPr oSerThrThrAsnThrTyrSerLeuGly                              645650655                                                                      LeuAlaGlyArgAlaTrpSerGlyGlyPheThrGlnSerAlaPheThr                               660 665670                                                                     ValLeuSerAspAlaArgPheLysThrAlaProGluValIleAspGlu                               675680685                                                                      LysIleLeuAspAlaT rpGluArgValGluTrpValSerTyrGlnTyr                              690695700                                                                      LeuAspArgIleGluValLysGlyLysAspGlyAlaArgTrpHisPhe                               705710 715720                                                                  GlyAlaValAlaGlnHisValIleSerValPheGlnAsnGluGlyIle                               725730735                                                                      AspValSer ArgLeuAlaPheIleCysTyrAspLysTrpAsnGluThr                              740745750                                                                      ProAlaGluTyrArgAspValThrGluGluGluHisSerAlaGlyVal                                755760765                                                                     TyrProLeuIleGlnThrLysValLeuValArgGluAlaValGluAla                               770775780                                                                      GlyGluCysTyrGly IleArgTyrGluGluAlaLeuIleLeuGluSer                              785790795800                                                                   AlaMetMetArgArgArgValLysLysLeuGluGluGlnValLeuGln                                805810815                                                                     LeuThrGlyAsn                                                                   820                                                                            (2) INFORMATION FOR SEQ ID NO: 3:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 29 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       ( D) TOPOLOGY: linear                                                          (ii) MOLECULE TYPE: Oligonucleotide                                            (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 3:                                       GATCCATATGACGGTCTCAACCGAAGTTG29                                                (2) INFORMATION FOR SEQ ID NO: 4:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 34 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                        (D) TOPOLOGY: linear                                                          (ii) MOLECULE TYPE: Oligonucleotide                                            (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 4:                                       GATCCATATGCTGATCCAGCGATGTTTTGGGTGG34                                           (2) INFORMATION FOR SEQ ID NO: 5:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 35 base pairs                                                      (B) TYPE: nucleic acid                                                          (C) STRANDEDNESS: single                                                      (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: Oligonucleotide                                            (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 5:                                       GATCCATATGCGTAATTATGTCGATGCTGCAATCG35                                          (2) INFORMATION FOR SEQ ID NO: 6:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 39 base pairs                                                      (B ) TYPE: nucleic acid                                                        (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: Oligonucleotide                                            (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 6:                                       GATCCATATGCGTGATGGTGTCAGCATTAAGGATTTTGG39                                      (2) INFORMATION FOR SEQ ID NO: 7:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 35 base pairs                                                       (B) TYPE: nucleic acid                                                        (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: Oligonucleotide                                            (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 7:                                       GATCAAGCTTATCAATTCCCTGTTAATTGCAAAAC35                                      

We claim:
 1. DNA fragment carrying a gene encoding an enzyme that fragments high molecular mass N-acetylheparosan and the expression systems permitting its biosynthesis, said DNA fragment having 3089 bp and corresponding to the nucleotide sequence SEQ ID N°
 1. 2. DNA fragment encoding the peptide sequence SEQ ID N°
 2. 3. DNA fragment encoding all or part of the peptide sequence SEQ ID N°
 2. 4. Strain carrying a plasmid permitting the production of a recombinant enzyme that fragments high molecular mass N-acetylheparosan, said strain being obtained by transforming the strain RRI of Escherichia coli (K12) or another equivalent strain, with a vector carrying a DNA fragment corresponding to the sequence SEQ ID N°
 1. 5. Strain deposited at the CNCM of the Institut Pasteur, Paris, France under the number 1-1352.
 6. The strain TP 2339 transformed with the plasmid p868,26.
 7. The plasmid p868,26. 